Viable Singularity-Free f(R) Gravity Without a Cosmological Constant (2009)
Miranda, Vinicius, Joras, Sergio E., Waga, Ioav, Quartin, Miguel
Several authors have argued that self-consistent $f(R)$ gravity models distinct from $\Lambda $CDM are almost ruled out. Confronting such claims, we present a particular two-parameter $f(R)$ model...
Dark Interactions and Cosmological Fine-Tuning (2008)
Quartin, Miguel, Calvao, Mauricio O., Joras, Sergio E., Reis, Ribamar R. R., Waga, Ioav
Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied,...
When did cosmic acceleration start? How fast was the transition? (2007)
Ishida, Emille E. O., Reis, Ribamar R. R., Toribio, Alan V., Waga, Ioav
Cosmic acceleration is investigated through a kink-like expression for the deceleration parameter (q). The new parametrization depends on the initial (q_i) and final (q_f) values of q, on the...
Challenges for scaling cosmologies (2006)
Amendola, Luca, Quartin, Miguel, Tsujikawa, Shinji, Waga, Ioav
A cosmological model that aims at solving the coincidence problem should show that dark energy and dark matter follow the same scaling solution from some time onward. At the same time, the model...
Observational Constraints on Silent Quartessence (2005)
Amendola, Luca, Waga, Ioav, Finelli, Fabio
We derive new constraints set by SNIa experiments (`gold' data sample of Riess et al.), X-ray galaxy cluster data (Allen et al. Chandra measurements of the X-ray gas mass fraction in 26 clusters),...
Observational Constraints on Chaplygin Quartessence: Background Results (2003)
Makler, Martin, De Oliveira, Sergio Quinet, Waga, Ioav
We derive the constraints set by several experiments on the quartessence Chaplygin model (QCM). In this scenario, a single fluid component drives the Universe from a nonrelativistic matter-dominated...
The end of unified dark matter? (2002)
Sandvik, Havard, Tegmark, Max, Zaldarriaga, Matias, Waga, Ioav
Despite the interest in dark matter and dark energy, it has never been shown that they are in fact two separate substances. We provide the first strong evidence that they are separate by ruling out a...
Constraints on the generalized Chaplygin gas from supernovae observations (2002)
Makler, Martin, De Oliveira, Sergio Quinet, Waga, Ioav
We explore the implications of type Ia supernovae (SNIa) observations on flat cosmological models whose matter content is an exotic fluid with equation of state, p=-M^(4(a+1))/rho^a. In this...
Waga, Ioav, Frieman, Joshua A.
We explore the implications of gravitationally lensed QSOs and high-redshift SNe Ia observations for spatially flat cosmological models in which a classically evolving scalar field currently...
We investigate observational constraints from lensing statistics and high-z type Ia supernovae on flat cosmological models with nonrelativistic matter and an exotic fluid with equation of state,...
Weak Gravitational Lensing by Voids (1998)
Amendola, Luca, Frieman, Joshua A., Waga, Ioav
We consider the prospects for detecting weak gravitational lensing by underdensities (voids) in the large-scale matter distribution. We derive the basic expressions for magnification and distortion...
Constraints from High Redshift Supernovae upon Scalar Field Cosmologies (1997)
Frieman, Joshua A., Waga, Ioav
Recent observations of high-redshift Type Ia supernovae have placed stringent constraints on the cosmological constant $\Lambda$. We explore the implications of these SNe observations for...